That's a big one. Basically, think of prayer more as communion with God or a turning of one's heart to Him, more than a laundry list of complaints and requests 8-)
Prayer. An exhaustive and exhausting treatment of the topic, but worth the effort.
...and a couple of times God repented (Ninevah, etc)?
And "changed His mind," and the like. Again, this is figurative speech. The "change of mind" represents more how God is perceived by human beings. Particularly in the Old Testament, a theologically naive people often anthropomorphized God.
God declares early in Scripture that HE CREATED MAN FOR FELLOWSHIP, RELATIONSHIP.
GOD HIMSELF CHOSE
that dialogue with those who truly loved Him could and would move His heart and His hand. That's part of what RELATIONSHIP is about.
In any case, it's part of God's design, HIS DESIRES.
I personally find it exceedingly fitting that God gets what God wants.